Re: [Discuss-gnuradio] OOT Decimation Module dropping data samples

[Michael Berman]

Martin,

Thank you for the quick response to my issue!

I cannot release the source code as is, however I can describe what I am doing, and possibly if need be I can release a deprecated version that still exhibits this behavior.

I am taking 1 MHz of spectrum and putting this through a 50 channel channelizer to obtain 20 kHz channels.  The signals I am interested in are all at +/- 5 kHz of 12 of the original 50 channels; the channels I am not using are fed into NULL sinks.  I then take my channels of interest and feed them through a mixer by multiplying the signals by a +/- 4950 Hz complex sinusoid to shift my signals of interest to +/- 50 Hz in each channel.  Each channel is then ran through an FIR filter and into an instance of the blocks at question.

I have set this up to run with just one channel instead of the 12 as described above and everything works fine, so I believe this may be an issue with having multiple instances of a block alive at the same time.  Are the input and output buffers thread safe against multiple instances of the same block running?

Michael

On Wed, Feb 26, 2014 at 1:42 AM, Martin Braun <address@hidden> wrote:

On 02/26/2014 01:31 AM, Michael Berman wrote:
> I am seeing some odd behavior with an OOT decimation block.  What I am
> seeing is chunks of data are being dropped down to noise for random
> calls of the work function in my OOT.  To observe this happening, I
> tee'd off the connection going into my OOT module and went strait into a
> file sink and then from within the OOT module for each call of the work
> function I stored off the incoming data to a file; the results of a good
> and bad frame of data are provided in the below links.  Within this
> data, the top chart is the file sink tee'd off and you can see it
> tracking well for the most part with the data from within the module on
> the bottom.  Within the "bad frame" image however, a little over 1000
> samples in, the data drops down noise around 0 instead of being a nice
> (and slightly noisy...) sinusoid.  The OOT module has a decimation value
> of 4000 in this particular case.  I am running on Fedora 20 with a week
> old pull of GNURadio master branch.
>
> Does anybody have any thoughts as to why this is happening, and what I
> could do to resolve it?

Agreed this is weird. No immediate solution pops to my mind, but can you
provide some more info:
- Is this block part of a larger flow graph, or does this occur also
when you isolate your block?
- Is this code you can share? If so, can we see the OOT

> The first resolution that is coming to mind would be to re-write my OOT
> module to run with general_work, and manage the input buffer myself.
>  Does anybody see any issues with doing this as a work around/solution?

There's no reason not to do that, but it would be a big surprise if that
helped. After all, a sync_decimator is just a very thin wrapper around a
gr::block.

> good frame: https://www.dropbox.com/s/tma3qn5byismgha/good_frame.png
> bad frame: https://www.dropbox.com/s/xgvcmlbgma14k0i/bad_frame.jpg
>
>
> Thank you all in advance for the help,
>
> Michael Berman
>
>
>

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